The present invention relates to a traffic environment recognition method and a system for carrying out the same and, more particularly to a traffic environment recognition method suitable for recognizing the traffic environment of a vehicle, and a traffic environment recognition system for carrying out the traffic environment recognition method to be loaded on a vehicle, such as an automobile.
Importance of active safety measures for recognizing the environment of a vehicle including lanes and other vehicles, detecting a condition that may cause an accident, and warning the driver of the vehicle to take measures for avoiding dangers or avoiding accidents by positively automatically controlling the vehicle has progressively increased. Various automotive traffic environment recognition systems have been proposed.
An active cruise control system (ACC system) has been commercially marketed. This ACC system measures the headway distance between the host vehicle and the preceding vehicle by using a laser radar or a millimeter wave radar, and accelerates or decelerates the host vehicle according to the measured headway distance to maintain safety vehicle spacing. Thus, the ACC system ensures the safe operation of the vehicle.
However, the laser radar or the millimeter wave radar (hereinafter referred to simply as “radar”) employed in the ACC system must operate on limited power to measure the headway distance between the host vehicle and the preceding vehicle traveling a long distance ahead. Therefore, the radar of the ACC system cannot use a vertically and horizontally wide beam. Consequently, it occurs sometimes that the beam of the radar passes through a space under the preceding vehicle when the preceding vehicle is a heavy truck and the ACC system fails in detecting the preceding heavy truck or that the host vehicle nose-dives and the ACC system fails in detecting the preceding vehicle when the host vehicle decelerates sharply to avoid collision against the sharply decelerated preceding vehicle or a cut-in vehicle.
Since the ACC system is provided with only a single radar and, sometimes, fails in detecting the preceding vehicle in case the host vehicle nose-dives. Thus, it is essential to the enhancement of the safety of the vehicle to measure the headway distance between the host vehicle and the preceding vehicle on the basis of detection signals provided by a plurality of sensors, and to improve the reliability of the ACC system.
Traffic environment recognition systems provided with a plurality of sensors are disclosed in, for example, Japanese Patent Laid-open Nos. 6-230115 (first reference), 11-44533 (second reference) and 2000-121730 (third reference). The traffic environment recognition system mentioned in the first reference determines a headway distance on the basis of an image formed by a camera, and a measurement provided by a millimeter wave radar, and uses the headway distance with higher reliability. For example, it is decided that the reliability of information provided by the camera is low in a rainy or foggy weather, and it is decided that the reliability of information provided by the millimeter wave radar is low when information about the road on which the host vehicle is traveling read from a road map of an automotive navigation system indicates a curve of a small radius or a narrow road. A headway distance determined on the basis of the information provided by the camera is used when it is decided that the reliability of the information provided by the camera is high or a headway distance determined on the basis of the information provided by the millimeter wave radar is used when it is decided that the reliability of the information provided by the millimeter wave radar is high.
The traffic environment recognition system mentioned in the second reference measures the headway distance between the host vehicle and the preceding vehicle by a radar, calculates the headway distance by a headway distance measuring unit on the basis of the measured headway distance, and controls the traveling speed of the host vehicle automatically by a vehicle speed control unit on the basis of the calculated headway distance. Meanwhile, an image input unit provides an image of a scenery extending ahead of the host vehicle, a measuring unit sets a template including a point corresponding to a position of distance measurement in the input image provided by the image input device, and a template image storage unit stores a template image included in the template in a storage device. When the radar is unable to measure distance, a control unit executes a control operation to make a correlation calculating unit determine an image area most analogous with the template image stored in the storage device by a correlation process, calculates an estimated position of the preceding vehicle at the center of the image area, and a headway distance calculating unit calculates a headway distance on the basis of the estimated position of the preceding vehicle.
The traffic environment recognition system mentioned in the third reference measures the headway distance between the host vehicle and the preceding vehicle by a millimeter wave radar, measures the width of the preceding vehicle by a laser radar in a state where both the millimeter wave radar and the laser radar are detecting the preceding vehicle, and uses a headway distance measured by the millimeter wave radar and a vehicle width previously measured by the laser radar in other states.
In a system disclosed in Japanese Patent Laid-open No. 2001-84485, a traffic sign or the like is set on a road extending ahead of a visible camera for detection data provided by a visible image sensor and a millimeter wave laser, a visible image-processing unit decides a self-detection ability according to the variation of environmental condition from an image of the traffic sign and provides the results of processing, a detection information selecting and processing unit selects automatically an output provided by a detectable vehicle detecting device, and the following operation is performed on the basis of selected detection information to detect abnormal traveling and stoppage.
Those prior art techniques have the following problems because the same uses information detected and provided by another sensor when the reliability of the single sensor is low.
(1) A decision must be made as to whether or not the same object is recognized.
(2) The decision needs a complicated procedure when there are a plurality of preceding vehicles or objects.
(3) The extensibility of the system is unsatisfactory in using other sensors including a navigation system in addition to the radar and the image-processing unit.
The prior art vehicle controller controls a vehicle for traveling on the basis of detection information provided by the plurality of sensors. However, the vehicle controller must decide whether or not the plurality of sensors detected the same object, which needs a complicated vehicle control algorithm, control performance is affected adversely, and the improvement of control function and reliability is difficult.